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Measuring Programs and Calibration

Druckmessungen in Trinkwasser- und Gasversorgungsnetzen

In recent years pressure measurements in drinking water and gas supply networks have gained vast importance. Against a background of increasingly pressing costs and the aging of networks many providers are required to optimize and to refurbish their networks. In order to tackle such a task strategically and purposefully requires a sound foundation. An important element of this foundation is a calibrated inventory of the network infrastructure, because informed decisions can be only made on the basis of a calibrated inventory of the network infrastructure and so paves the way for the future.

We support you in this task with our expertise, our experience and our technical equipment. We support you from the planning and accompaniment during measuring programs with the calibration of the network inventory up to the design of the envisaged network - tailored to your specification. We can offer you a comprehensive and technically advanced performance package.

Measurement programs in drinking water networks

For measurements in drinking water networks selected hydrants are equipped with pressure data loggers. While maintaining operational safety and the required minimum pressures the greatest possible pressure losses are simulated by a withdrawal at other selected hydrants.These pressure losses are recorded by the pressure loggers and can be analysed later for the calibration of the network.

Our experience tells us that the following points need to be observed in order to achieve transparent, plausible, and useful measurement results with which a fine calibration can be performed:

  • Measurements are taken at night, when flows in the network are at a minimum (preferably between 1:00 to 4:00 AM).
  • The number of loggers is best limited to 20 to 30 units, so that the installation can be done an in one day.
  • Accordingly the study area is to be limited in size.
  • The draw-off time at the hydrants should be about 10 to 15 minutes, so that the pressure can stabilise and an as contestant as possible draw-off be achieved.
  • The pressure data loggers are installed in one day and removed again the next day or immediately after the completion of the measurements.

If pressure measurements are carried out during the day hours, the outer limit for the calibration is not clearly defined due to the spatially differential draw-off. This leads to considerable uncertainty and consequently to errors in the calibration. Such errors can be excluded by taking measurements at night.

 

Programs for the measurement in gas supply networks

For measurements in gas supply networks initially all feeder stations will be equipped with pressure data loggers. In addition to the pressure data loggers ideally volumetric meters are to be installed to capture flow rates. In addition data loggers are installed at selected locations along the network, usually at the consumer connection point. Similar to the measurements in drinking water networks, maximum pressure losses in the network are aimed at, measuring programs can therefore be carried out only in times of high draw-off. The measurements are thus commonly limited to the months of December to March (in the northern hemisphere).

In order to achieve meaningful measurement results, the choice of representative measuring points are of particular importance. The following points are particularly to be considered:

  • Installation at bulk supply lines and at endpoints
  • Increase the number of loggers in areas of known weak pressure
  • Adherence to a density of 3 to 4 measuring points per 10 km

Generally measuring points with network pressure must be freely accessible. "Inactive" house connections are ideal for this purpose. If these are not available, the measuring points are set up at the shortest available house connections of single residential or duplex dwellings. In order to increase the chances for capturing pressures in the network during times of peak consumption, measurement programs with duration of at least 2 to 3 weeks need to be envisaged.

Druckmessungen in Trinkwasser- und Gasversorgungsnetzen

Calibration of network models

Network calibration is the comparison of results of computations in a technical model with actual measurements during operational conditions. In the case of drinking water and gas supply systems, this means adjusting the calculated pressures in the network model to closely match the actually measured pressures. Reference values for permissible error margins are laid down in DVGW worksheet GW 303-1.

Generally adjustments in a model are made to not directly measurable quantities such as the roughness coefficient of pipes, local pressure drops or even the inside diameters (e.g. reductions caused by mineral deposits). In the case of drinking water networks the aperture of valves (open, partially open, closed) plays in many cases an important role when calibrating the network.

"The roughness coefficient of existing pipelines and pipe networks is in principle determined by comparing actual measurements with comparable calculations."(DVGW GW 303-1, 2006). This principle implies the need of model calibration. The number of measurement points required for model calibration may vary depending upon the length of the network and the objectives to be achieved with the model calibration.

Detailed fine calibration usually requires a very dense network of measuring points with temporal maximum resolution recording of operating conditions. With the number of pressure capsules at our disposal, we are able to measure networks of over 100 km (corresponding to the requirements in line with DVGW GW 303-1, 2006).

Druckmessungen in Trinkwasser- und Gasversorgungsnetzen